:welcome: I'm not familiar with hydroponic but seedlings, typically, do not need nutrients. You could have fert burn. I don't believe that your lighting will be burning the leaves, either. Others will chime in soon...
I have read that a plant does not know the difference between synthetic nitrogen and organic nitrogen - nitrogen is nitrogen to the plant. I am not a botanist so I don't know if it's true.
Sorry, I was referring to Calamari Kid's comment. I don't believe that rain/water will act as a magnifying agent. If true, summer rain would destroy leaves because we don't wipe them off after a rain shower. Kinda time consuming :)
I bought two bags in late March and though it's early, I'm very happy with it. Light, drains well and a great price. I amended mine with bat guano and Tomato Tone.